1. Field of the Invention
The invention relates to a system for detecting free particles in a component housing and to its detection method.
2. Discussion of the Background
The principle of searching for particles in the housings of individual electronic components is known in the art. It is put into practice, at the present time, by the piezo-acoustic detection of the impacts which these particles generate on the walls of the housing when the component is subjected to a vibration of appropriate amplitude and frequency Appliances which generate a sequence of shocks (to free possibly "wedged" particles) and which provide standardized detection periods have been on the market for several years. Particles of a mass of 10.sup.-6 gram can be detected by this method.
This method is, above all, a means for improving the production processes for components; but it is also the last stage in combatting pollution which may be dangerous for the proper functioning of the component and which is generated or trapped during the closing of its housing.
This test is often required for components to be used in space. However, it is carried out before the components are assembled on printed-circuit boards.
When the components are mounted on printed-circuit cards, it becomes difficult to conduct such a test because of the risks of damage to the card during this handling.
The identification of components polluted by particles and assembled on a fully equipped printed card becomes expedient from the moment before one of these components has been involved in a failure process.
It becomes necessary when:
this pollution is found to be of metallic origin,
there is sufficient probability of the presence of an identical source of pollution in the rest of the batch of components,
the function performed in the equipment necessitates exceptional reliability,
the time and financial resources for producing one or more new cards are not available.
The test of components already assembled on printed-circuit cards is made difficult because:
the equipped cards are of different formats,
the cards are difficult to hold mechanically,
the components involved are in metal housings of the type TO99 (8.2 mm in diameter and 4 mm high), and access to some of them is difficult,
the cards are lacquered on both sides,
no mechanical, physical or chemical deterioration of the cards is acceptable,
the detection of the polluted components must
it must be easy for the system as a whole to be used within an industrial context.